The sport of archery contains many variables which the archer must learn to deal with on a consistently accurate basis in order to be successful. In order for the archer's arrow to strike the target at the point of aim, he must make the necessary horizontal and vertical adjustments for windage and elevation, respectively. In addition he must also be sure that he does not cant the bow to the left or the right. He must also be sure to draw the bow to the same anchor point every time he shoots. If the correct adjustments are not made to accurately control any or all of these variables, then the arrow will most certainly not strike the point of aim. Generally, the archer only aquires the skills necessary to accurately control these variables through experience.
In order for the archer to make the correct vertical adjustment for elevation, he must first be able to accurately judge the distance or range to the target. Of all the variables mentioned above, this is generally considered to be the most difficult task facing the archer, whether it be on the practice range or in an actual hunting situation. Generally, most archers learn to judge the correct distance to the target only by spending long hours in the practice field. However, the optical illusions that can be created by shooting uphill or down hill, or across a depression such as a small canyon, are astounding. Even an experienced archer can misjudge the distance drastically. Thus, a need has been felt for a rangefinding device which is accurate, attaches easily to the bow, and is convenient to use.
Several types of rangefinding devices which attach to the archer's bow are available. These devices and the methods used for finding the range are described in the following patents: Spencer, U.S. Pat. No. 3,945,127 (1976); Duerst, U.S. Pat. No. 4,325,190 (1982); Mann and Schultz, U.S. Pat. No. 4,170,071 (1979); Larson, U.S. Pat. No. 3,696,517 (1972).